Sarah received $\$55$ for her birthday. She used some of that money to buy $3$ shirts priced at $m$ dollars each. How much money does Sarah have left? Write your answer as an expression. $\$$
Solution: Let's see what happens as the price of each shirt increases: Price of each shirt Amount of money left ${5}$ $55-3 \cdot {5} = 40$ ${6}$ $55-3 \cdot {6} = 37$ ${7}$ $55-3 \cdot {7} = 34$ Price of each shirt Amount of money left ${m}$ $55-3 \cdot {m} = 55-3m$ The answer: $55-3m$